Generally, a liquid crystal display device controls the light transmissivity of a liquid crystal by use of an electric field, thereby displaying a picture or other visual data. For this purpose, the liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in an active matrix shape, and a drive circuit to drive the liquid crystal display panel.
The liquid crystal display device, as shown in FIG. 1, includes a liquid crystal display panel 6 to display a picture in accordance with the polarity pattern of a pixel signal; a data drive integrated circuit D-IC 10 to drive data lines of the liquid crystal display panel 6 is mounted on a data tape carrier package TCP 8; a gate drive integrated circuit D-IC 12 to drive gate lines of the liquid crystal display panel 6 is mounted on a TCP 4; and a timing controller 30 to control the driving of the plurality of data D-ICs 10 and the plurality of gate D-ICs 12.
The liquid crystal display panel 6 includes a liquid crystal layer formed between an upper substrate 5 and a lower substrate 3, and a spacer to maintain a fixed distance between the upper substrate 5 and the lower substrate 3. A color filter, a common electrode, a black matrix and soon are formed in the upper substrate 5 of the liquid crystal display panel 6, as is known in the art. The common electrode can be formed on the lower substrate 3. Further, the lower substrate 3 of the liquid crystal display panel 6 includes a thin-film transistor (TFT) formed at each of intersections of the gate lines and the data lines, and a liquid crystal cell connected to the thin-film transistor. A gate electrode of the thin-film transistor is connected to any one of the horizontal gate lines, and a source electrode is connected to any one of the vertical data lines. The thin-film transistor supplies a pixel signal from the data line to the liquid crystal cell in response to a scan signal from the gate line. The liquid crystal cell includes a pixel electrode connected to a drain electrode of the thin-film transistor, and a common electrode facing the pixel electrode with a liquid crystal layer therebetween. The liquid crystal cell drives the liquid crystal layer in response to the pixel signal supplied to the pixel electrode, thereby controlling the light transmissivity.
In order to drive the liquid crystal cells on the liquid crystal display panel 6, inversion driving methods such as a frame inversion system, a line inversion system and a dot inversion system are used. In the driving method of the frame inversion system, the polarity of the pixel signals supplied to the liquid crystal cells on the liquid crystal display panel 6 is inverted from frame to frame. In the line inversion driving method, the polarity of the pixel signals supplied to the liquid crystal-cells is inverted in accordance with the line on the liquid crystal display panel 6. The dot inversion system has a polarity of the pixel voltage signal supplied which is opposite to the polarity of the pixel signal voltage supplied to the liquid crystal cells that are adjacent to the liquid crystal cells on the liquid crystal display panel 6 in the vertical and horizontal directions The polarity of the pixel signals supplied to all the liquid crystal cells on the liquid crystal display panel 6 is inverted from frame to frame. Such an inversion method is performed by having the data D-IC 10 responded in accordance with a polarity signal POL supplied to each of the data D-IC 10 from the timing controller 30.
The liquid crystal display device is driven at a frame repetition frequency of 60 Hz. But, in a system like a notebook which consumes low power it is necessary to lower the frame repetition frequency to 50˜30 Hz. As the frame repetition frequency gets lower, a Greenish optical phenomenon is generated even in the dot inversion system which may provide the best picture quality among the inversion methods. Horizontal 2-dot inversion systems and square inversion systems have also been suggested.
In the horizontal 2-dot inversion system, the polarity of the pixel signal is changed for one dot in a vertical direction, while it is changed for two dots in a horizontal direction and, in addition, the polarity of the pixel signals supplied to all the liquid crystal cells on the liquid crystal display panel 6 are inverted from frame to frame. In the square inversion system, the polarity of the pixel signal is changed for two dots in a vertical direction and it is also changed for two dots in a horizontal direction and, in addition, the polarity of the pixel signals supplied to all the liquid crystal cells on the liquid crystal display panel 6 is inverted from frame to frame.
In this way, in case of the one dot inversion system, the polarity of the pixel signal supplied to the liquid crystal cell repeats for the two liquid crystal cells in the horizontal direction. On the other hand, in case of the two dot inversion system, the polarity of the pixel signal supplied to the liquid crystal cell repeats for four liquid crystal cells in the horizontal direction, and in case of the square inversion system, the polarity of the pixel signal supplied to the liquid crystal cell repeats by for four liquid crystal cells in the vertical and horizontal directions.
The timing controller 30 generates gate control signals such as GSP, GSC, GOE and so on, which control the drive of the gate D-IC 4, and generates data control signals such as SSP, SSC, SOE, POL and so on, which control the drive of the data IC 10. Further, the timing controller 30 aligns the data signal supplied from the system to fit the data signal for the drive of the liquid crystal display panel 6, and supplies the aligned data signal to a plurality of data D-IC 10.
The timing controller 30 is mounted on a data PCB (printed circuit board) 20. The data PCB 20 is connected to an external system through a user connector. On the data PCB 20, signal lines are formed to supply various control signals and data signals from the timing controller 30 to each of the data D-IC 10 and the gate D-IC 12.
Each of the gate D-IC 12 is mounted on gate TCP 4. The gate D-IC 12 mounted on the gate TCP 4 is electrically connected to the gate pads of the liquid crystal display panel 6 through the gate TCP 4. The plurality of gate D-IC 12 sequentially drives the gate lines of the liquid crystal display panel 6 during one horizontal period (1H). The gate TCP 4 is connected to a gate PCB 26. The gate PCB 26 supplies the gate control signals from the timing controller 30 through the data PCB 20 to the plurality of gate D-IC 12 through the gate TCP 4.
Each of the data D-IC 10 is mounted on each of the data TCP 8. The data D-IC 10 mounted on the data TCP 8 is electrically connected to the data pads of the liquid crystal display panel 6 through the data TCP 8. The data D-IC 10 convert digital pixel data into an analog pixel signal to supply the converted pixel signal to the data lines of the liquid crystal display panel 6.
In this way, in the driving device of the related art liquid crystal display device, the repetition period of the pixel signal polarity becomes uniform or non-uniform in accordance with the number of the output channels of the data D-IC 10 and the inversion method of the polarity pattern of the pixel signal supplied to the liquid crystal display panel 6.
Specifically, the data D-IC 10 having even-numbered output channels might output signal voltages such that the polarity of the pixel signal has the polarity pattern of the one dot inversion system regardless of the number of output channels of the data D-IC 10. As shown in FIG. 2, when the pixel signal having the polarity pattern of the one dot inversion system is supplied to the liquid crystal display panel 6 by use of the data D-IC 10 having 384 (a multiple of 4) output channels (Ch1 to Ch384), the polarity of the pixel signal between the last output channel Ch384 of the odd-numbered data D-IC 10 and the first output channel Ch1 of the even-numbered data D-IC 10 is not equal but inverted. That is, the polarity of the pixel signal outputted from the last output channel Ch384 of the odd-numbered data D-IC 10 is “−”, and the polarity of the pixel signal outputted from the first output channel Ch1 of the even-numbered data D-IC 10 is “+”.
Also, in case that the pixel signal having the polarity pattern of the one dot inversion system is supplied to the liquid crystal display panel 6 by use of the data D-IC 10 having 414 (a multiple of 2, but not a multiple of 4) output channels (Ch1 to Ch414), the polarity of the pixel signal between the last output channel Ch384 of the odd-numbered data D-IC 10 and the first output channel Ch1 of the even-numbered data D-IC 10 is not equal but inverted. Accordingly, the driving method of the liquid crystal display panel 6 by the one dot inversion system in use of the data D-IC 10 having the output channels, which are a multiple of 2 and not a multiple of 4, is driven to have the polarity pattern of the exact one dot inversion system.
As shown in FIG. 3, in case of the pixel signal having the polarity pattern of the horizontal two dot inversion system is supplied to the liquid crystal display panel 6 by use of the data D-IC 10 having 384 (a multiple of 4) output channels (Ch1 to Ch384), the polarity of the pixel signal between the last two output channels Ch 383, Ch384 of the odd-numbered data D-IC 10 and the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 is not equal but inverted. In other words, the polarity of the pixel signal outputted from the last two output channels Ch383, Ch384 of the odd-numbered data D-IC 10 is “−−”, and the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 is “++”. Accordingly, the driving method of the liquid crystal display panel 6 by the two dot inversion system in use of the data D-IC 10 having the output channels, of which the number is the multiple of 4, is driven to have the polarity pattern of the exact horizontal two dot inversion system.
On the other hand, as shown in FIG. 4, in case that the pixel signal having the polarity pattern of the horizontal two dot inversion system is supplied to the liquid crystal display panel 6 by use of the data D-IC 10 having 414 (a multiple of 2, but not a multiple of 4) output channels (Ch1 to Ch414), the polarity of the pixel signal between the last two output channels Ch 413, Ch414 of the odd-numbered data D-IC 10 and the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 is equal. Specifically, in case that the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of the data D-IC 10 having the output channels, of which the number is the multiple of 2, starts with “++”, the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of each of the odd-numbered data D-IC 10 and the even-numbered data D-IC 10 starts with “++”. Hence, the polarity of the pixel signal outputted from the last two output channels Ch413, Ch414 of the odd-numbered data D-IC 10 is “++”, and the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 is “++”. Accordingly, in case of driving the liquid crystal display panel 6 by the two dot inversion system in use of the data D-IC 10 having a number of output channels which is a multiple of 2, the same polarity of pixel signal is supplied to the four liquid crystal cells which are a bordering area between the adjacent data D-IC 10.
Therefore, as shown in FIG. 4, in case that the number of the output channels of the data D-IC 10 is a multiple of 2 but not a multiple of 4, the repetition period of the pixel signal polarity is non-uniform at a bordering area A between the adjacent odd and even data D-IC's 10 and may result a picture quality defect such as a vertical line in the liquid crystal display device using the related art horizontal two dot inversion system.
As shown in FIG. 5, in case that the pixel signal having the polarity pattern of the square inversion system and where the data D-IC 10 have 414 (a multiple of 2, but not a multiple of 4) output channels Ch1 to Ch414, the polarity of the pixel signal between the last two output channels Ch 413, Ch414 of the odd-numbered data D-IC 10 and the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 of jth (but, j is a positive integer) and (j+1)th horizontal lines is equal. Specifically, in case that the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of the data D-IC 10 having the output channels, the number of output channels being a multiple of 2, starts with “++”, the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of each of the odd-numbered data D-IC 10 and the even-numbered data D-IC 10 of each of the jth and (j+1)th horizontal lines starts with “++”. As such, the polarity of the pixel signal outputted from the last two output channels Ch413, Ch414 of the odd-numbered data D-IC 10 of each of the jth and (j+1)th horizontal lines is “++”, and the polarity of the pixel signal outputted from the first and second output channels Ch1, Ch2 of the even-numbered data D-IC 10 of each of the jth and (j+1)th horizontal lines is “++”. Accordingly, in case of driving the liquid crystal display panel 6 by the square inversion system in use of the data D-IC 10 having output channels, the number of output channels being a multiple of 2 but not of 4, the same polarity of the pixel signal is supplied to the eight liquid crystal cells which are a bordering area between the adjacent data D-IC's 10.
Therefore, as shown in FIG. 5, in case that the number of the output channels of the data D-IC 10 is not a multiple of 4, the repetition period of the pixel signal polarity is non-uniform at a bordering area A between the adjacent data D-IC 10 and results in a picture quality degradation such as a vertical line in the liquid crystal display device using the related art square inversion system.